Abstract: The thermodynamic properties of microemulsion formed by six kinds of alkyl aryl sulfonates(AAS, synthesized in the laboratory) in the multi-component systems were investigated by dilution method. The influences of molecular structure, temperature, short chain alcohol, water content and salt concentration were respectively discussed. The results show that the increase of long alkyl carbon atom number(in alkyl aryl sulfonate molecule) causes the ΔG0o→i of the AAS/n-butanol/n-decane/water microemulsion systems decrease, along with the increase of the ΔS0o→i, and facilitates the formation of the microemulsion. The ΔS0o→i and carbon atom number of alkyl chain are in linear relationship, with ΔS0o→i=1.7975n+71.538. The ΔH0o→i is a constant. As the aromatic rings shift from the edge to the middle of the long carbonic chains, the ΔG0o→i of the microemulsion systems decreases, along with the decrease of ΔS0o→i and ΔH0o→i, facilitating the formation of the microemulsion. With the increase of temperature, ΔG0o→i of the microemulsion systems increase, hindering the formation of the microemulsion. The increase of carbon atom number of the alcohol causes ΔG0o→i decrease, which enables the formation of the microemulsion. ΔG0o→i and carbon atom number of the alcohol are in linear relationship, with ΔG0o→i=-2790.8n+7286.4(328 K). The increase of water content causes ΔG0o→i increase and the formation ability of the microemulsion decreases. ΔG0o→i and the volume of water are in linear relationship, with ΔG0o→i=6697.8V-7170.4(318 K). The increase of salt concentration causes ΔG0o→i decrease, and the formation ability of the microemulsion increases.

Key words: alkyl aryl sulfonate, structer, microemulsion, standard thermodynamic functions